1. Technical Field
The present disclosure relates to a base station device, a mobile station device, and a communication method.
2. Description of the Related Art
Transmitting not only audio data but large-sized data such as still image data, moving image data, and so forth, over cellular mobile communication systems, has become commonplace in recent years, as multimedia has become a more common form of information. In Long Term Evolution Advanced (LTE-Advanced), there is active study ongoing to realize high transmission rates using wireless broadband, Multiple-Input Multiple-Output (MIMO) transmission technology, and interference control technology.
There further is being undertaken study in LTE-Advanced to install small cells which are base station devices with low transmission power (also called “e Node B (eNB) cells, hereinafter referred to simply as “base station”) to realize high transmission rates at hot spots. Now, a case where a small cell, and a micro cell which is a base station with high transmission power, use the same frequency band, will be referred to as a “small cell scenario 1”. A case where a small cell and a micro cell use different frequency bands will be referred to as a “small cell scenario 2”. A case where no micro cell exists and only a small cell exists will be referred to as a “small cell scenario 3” (e.g., see 3GPP TR 36.842 V0. 2.0, “Study on Small Cell Enhancements for E-UTRA and E-UTRAN—Higher layer aspects”).
An arrangement relating to small cells is being studied regarding allocating resources of multiple base stations, connected to mobile station devices (sometimes also referred to as User Equipment (UE); hereinafter referred to simply as “mobile station”) via non-ideal backhaul. This is called “dual connectivity”. In dual connectivity, a base station that manages mobility of a mobile station is called a “Master eNB” (eNB is an abbreviation of “evolved Node B”), which is abbreviated to “MeNB”, and base stations other than the MeNB that allocate resources to mobile stations are called “Secondary eNB” (SeNB). A mobile station can use resources of both MeNB and SeNB.
The following four are conceivable as capabilities of mobile stations to which dual connectivity is applied.    a) Single Rx/Tx (which means a UE having a single Rx and a single Tx chain)    b) Single Rx/Multiple Tx    c) Multiple Rx/Single Tx    d) Multiple Rx/Tx (which means a UE having multiple Rx and multiple T×chains)
Specifically, Multiple Rx means the mobile station being able to simultaneously receive signals from an MeNB and signals from an SeNB. On the other hand, Single Rx means that the mobile station is not able to simultaneously receive signals from an MeNB and signals from an SeNB. In other words, the mobile station has to switch between receiving signals from the MeNB and the SeNB in a case of Single Rx. Further, Multiple Tx means that the mobile station is able to simultaneously transmit signals to the MeNB and to the SeNB. On the other hand, Single Tx means that the mobile station is not able to simultaneously transmit signals to the MeNB and the SeNB. In other words, the mobile station has to switch between transmitting signals to the MeNB and the SeNB in a case of Single Tx.
The following subframes have to be decided in order for a mobile station having the above-described Single Rx/Tx capability to support dual connectivity in a time division duplex (TDD) system, namely, subframe for transmission/reception to/from the MeNB (hereinafter may be referred to as “MeNB subframe”), and subframe for transmission/reception to/from the SeNB (hereinafter may be referred to as “SeNB subframe”). A method of allocating MeNB subframes and SeNB subframes to a mobile station that communicates with a base station by switching between MeNB and SeNB has been proposed (e.g., “Challenges in the uplink to support dual connectivity,” Intel Corporation, hereinafter referred to as “Intel”). Intel discloses one of multiple configuration patterns defining communication timing of uplink and downlink (UL-DL configurations) in communication frames, this one being Config#1. Intel describes that multiple UL subframes that are consecutive in a Config#1 communication frame are allocated to the same eNB, with MeNB subframes being switched to SeNB subframes and the timing of switching from UL subframes to DL subframes.
However, the arrangement described in Intel has a problem in that resource (subframe) allocation is inflexible, due to consecutive UL subframes included in a communication frame being allocated to the same eNB.